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Abstract:

An optical lens, especially an optical lens for mobile phones or image
sensors such as CCD (Charge Coupled Device) or CMOS (Complementary Metal
Oxide Semiconductor) is formed by a two-piece lens featuring high
performance, minimized total length and low cost.

Claims:

1. A two piece type optical lens comprising:a first lens element with
positive refractive power that is a meniscus aspherical lens having a
convex surface on an object side;a second lens element with positive
refractive power that is a meniscus aspherical lens having a convex
surface on an image side;an IR(infrared) cut-off filter; andan image
sensor arranged along an optical axis in order from the object
side;wherein following expressions are
satisfied:0.2f≦d<1f;0<|R3|≦100f;0.01<|f2|/|f1|<-
3; and20.ltoreq.Vd≦85;wherein f is an effective focal length of the
optical lens, d is the distance between the object side of the first lens
element and the image side of the second lens element, R3 is a radius of
curvature of the object side of the second lens element, f1 is an
effective focal length of the first lens element, f2 is an effective
focal length of the second lens element and Vd is Abbe's number of the
first lens element as well as the second lens element.

2. The two piece type optical lens as claimed in claim 1, wherein at least
one of the convex surface and a concave surface of the meniscus first
lens element is an aspherical surface.

3. The two piece type optical lens as claimed in claim 1, wherein at least
one of the convex surface and a concave surface of the meniscus second
lens element is an aspherical surface.

4. The two piece type optical lens as claimed in claim 1, wherein a
pre-aperture is disposed on the optical lens.

5. The two piece type optical lens as claimed in claim 1, wherein the an
aperture stop of the optical lens is arranged on front of the convex
surface on the object side of the first lens element.

6. The two piece type optical lens as claimed in claim 1, wherein the
first lens element is made of molded glass.

7. The two piece type optical lens as claimed in claim 1, wherein the
second lens element is made of molded glass.

8. The two piece type optical lens as claimed in claim 1, wherein the
IR(infrared) cut-off filter is made of glass with thickness of 0.145 mm.

Description:

BACKGROUND OF THE INVENTION

[0001]The present invention relates to a two piece type optical lens,
especially to an optical lens for mobile phones or image sensors such as
CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide
Semiconductor) formed by a two piece of lens with features of high
performance, minimized total length and low cost.

[0002]Along with advanced technology, electronics become more compact and
multifunctional. Besides digital still cameras, PC (personal computer)
cameras, network cameras and mobile phones, even persona digital
assistants are equipped with image capturing devices such as lens. For
meeting requirements of easy-carrying and humanization design, the image
capturing device not only need to have good imaging quality but also need
to have compact volume and lower cost so as to extend applications
thereof. Especially for applications on mobile phones, the requirements
above mentioned are much more important.

[0003]There are various materials available for producing conventional
spherical ground glass lens. Moreover, the spherical ground glass lens is
better for correcting chromatic aberration so that it is adapted widely.
Yet it's difficult to correct aberrations such as spherical aberration or
astigmatism for the spherical ground glass lens with smaller F Number and
larger field angle. In order to improve above shortcomings of
conventional spherical ground glass lens, aspherical plastic lens or
aspherical molded glass lens is applied to the image capturing devices
available now so as to obtain better imaging quality. For example, refer
to the lenses disclosed in U.S. Pat. No. optical image pick-up lens, U.S.
Pat. No. 6,031,670, wide-angle lens or Japanese patent P2001-183578A,
imaging lens etc. However, the total length of the above image capturing
devices is still too long. For example, in the lens set disclosed in
Japanese patent P2001-183578A, imaging lens, the distance d between a
firs surface of the first lens element and a second surface of the second
lens element is no less than 0.9f ( d≧0.9f, f is an effective
focal length of an optical lens assembly according to the present
invention ) so that the volume of the lens can't be reduced . Neither
does the cost. Such kind of design can't satisfy compact and light
requirements of electronics. Furthermore, applications of such lens are
limited severely, especially on mobile phones.

SUMMARY OF THE INVENTION

[0004]It is therefore a primary object of the present invention to provide
a two piece type optical lens that includes a first lens element with
positive refractive power, a second lens element with positive refractive
power, an IR cut-off filter and an image sensor arranged along an optical
axis in sequence from an object side. The first lens element and the
second lens element are both meniscus aspherical molded glass lens while
a convex surface of the first lens element is on the object side and a
convex surface of the second lens is on the image side. Moreover, the two
piece type optical lens satisfies following conditions:
0.2f≦d<1f, 0<|R3|100f, 0.01<|f2|/|f1|<3, and
20≦Vd≦85, wherein f is an effective focal length of the
whole lens; d is the distance between a convex surface on the object side
of the first lens element and a convex surface on the image side of the
second lens element; R3 is a radius of curvature of the object side of
the second lens element, f1 is an effective focal length of the first
lens element, f2 is an effective focal length of the second lens element
and Vd is Abbe's number of the first lens element as well as the second
lens element. Thereby a two piece type optical lens with high resolution
and minimized total length is formed.

[0005]It is another, object of the present invention to provide a single
piece type optical lens in which a pre-aperture is disposed on the
optical lens. An aperture stop is arranged on front of the convex surface
on the object side so as to effectively minimize total length of the lens
for increasing applications of the lens.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is a schematic drawing of an optical structure of an
embodiment according to the present invention;

[0007]FIG. 2 is a schematic drawing of a light path of an embodiment
according to the present invention;

[0008]FIG. 3 is a transverse ray fan plot in different field (true image
size 0, 0.355, 0.71, 1.065, 1.42 mm) of an embodiment according to the
present invention;

[0009]FIG. 4 shows field curvature of an image of an embodiment according
to the present invention;

[0010]FIG. 5 shows distortion of an image of an embodiment according to
the present invention;

[0012]FIG. 7 is a graph showing relative illumination generating by full
field toward zero field of an embodiment according to the present
invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013]A two piece type optical lens according to the present invention
includes a first lens element with positive refractive power L1, a second
lens element with positive refractive power L2, an IR(infrared) cut-off
filter 3 and an image sensor 4 arranged along an optical axis in order
from an object side. While imaging, firstly light passes the first lens
element L1, the second lens element L2 and the IR cut-off filter 3, then
an image is formed on a sensing surface 41 of the image sensor 4, as
shown in FIG. 2.

[0014]The first lens element L1 is a meniscus molded glass lens whose
convex surface 11 is on the object side while at least one of the convex
surface 11 and a concave surface 12 is an aspherical surface. The second
lens element L2 is a meniscus molded glass lens whose convex surface 21
is on the image side while at least one of the convex surface 21 and a
concave surface 22 is an aspherical surface. Moreover, a pre-aperture is
disposed on the optical lens of the present invention and aperture stop
13 is arranged on the convex surface 11 of the object side of the first
lens element L1 as shown in FIG. 1 & FIG. 2.

[0016]d is the distance between the convex surface 11 on the object side
of the first lens element L1 and the convex surface 21 on the image side
of the second lens element L2;

[0017]R3 is a radius of curvature of the object side of the second lens
element L2;

[0018]f1 is an effective focal length of the first lens element L1;

[0019]f2 is an effective focal length of the second lens element L2; and

[0020]Vd is Abbe's number of the first lens element L1 as well as the
second lens element L2.

[0021]In accordance with the structure mentioned above, the optical lens
according to the present invention has features of high resolution and
minimized total length so that the optical lens has smaller volume and
lower cost, both improving applications of the optical lens.

[0022]Refer to list one, the list includes data of surface number (#) in
order from the object side, type of each surface, the radius of curvature
R (mm), the on-axis surface spacing D (mm) and materials that the lens
made of.

[0027]The first lens element L1 and the second lens element L2 of the
embodiment are made of N-SK57 type molded glass lens while the IR cut-off
filter 3 is made of BK7 optical glass with thickness of 0.145 mm.

[0028]When the effective focal length f of the whole optical lens
according to the present invention is 2.07268 mm and distance between the
convex surface 11 (object side) of the first lens element L1 and the
convex surface 21 (image side) of the second lens element L2 is 1.31 mm,
a relational expression 0.2f≦d<1f is satisfied. When the radius
of curvature of the concave surface 22 (object side) of the second lens
element L2 R3 is -3.580208 mm, the condition of 0<|R3|≦100f is
satisfied. When the effective focal length of the first lens element L1
f1 is 2.284 mm, the effective focal length of the second lens element L2
f2 is 6.719 mm and |f2|/|f1|=2.942, the condition of
0.01<|f2|/|f1|<3 is satisfied. When the Abbe's number of the first
lens element L1 as well as the, second lens element L2 Vd is 59.6, the
condition of, 20≦Vd≦85 is satisfied. Refer from FIG. 3 to
FIG. 7, together with the list one and the list two, it is learned that
the total length of the optical lens according to the present invention
is 2.52527 mm.

[0029]Additional advantages and modifications will readily occur to those
skilled in the art. Therefore, the invention in its broader aspects is
not limited to the specific details, and representative devices shown and
described herein. Accordingly, various modifications may be made without
departing from the spirit or scope of the general inventive concept as
defined by the appended claims and their equivalents.

Patent applications by San-Woei Shyu, Taipei TW

Patent applications in class Including a nonspherical surface

Patent applications in all subclasses Including a nonspherical surface